The long range objective of the proposed research is to understand the molecular and structural basis of cytoplasmic streaming and cell contractility. Recent work suggests several common features at the molecular level between some forms of cytoplasmic streaming and muscle contraction. To pursue these similarities in more detail it is proposed to A: purify the myosin component from purified actomyosin of Physarum polycephalum, a classical material for the study of streaming. This will permit three separate studies, namely 1) examination of the myosin by electron microscopy for new data on the nature of the filaments which form at low ionic strength (negative staining technique), 2) examination of properties of the cross-reaction product of Physarum myosin and actin of vertebrate striated muscle, 3) study of the light chains sulfhydryl content and methylated residues of myosin. On the other hand the unusual properties reported for the actin of Physarum may be related to the molecular differences between muscle contraction and streaming. To study these it is planned to B: prepare the actin component from Physarum by two independent methods to confirm the disputed magnesium polymer form of this actin. If successful, a study will be made of conditions favoring the formation of this polymer from F-actin polymer. In transferring we wish to also: study calcium regulation of this actomyosin complex.